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Non-rust diseases
VIRAL SILENCING SHEDS LIGHT
ON DISEASE RESISTANCE
the australian national university’s dr Peter solomon is using a special viral silencing method
to switch off the genes in wheat plants that render them susceptible to Septoria nodorum
blotch, which could lead to the development of wheat varieties with durable resistance
By Janet Paterson
AUSTRALIAN NATIONAL
UNIVERSITY geneticist Dr Peter
Solomon says the decision by the GRDC
to sequence the Septoria nodorum blotch
(SNB) genome in 2004 showed great
foresight and has enabled his research
team to unravel how the pathogen
causes disease at a molecular level.
"Having the SNB genome sequence
actually averted us from continuing down
the wrong path in our quest for resistance
to this costly disease," Dr Solomon says.
The team was initially chasing true
resistance genes for the disease, similar
to that operating in rust resistance.
"We thought we were looking for
the lock on the wheat genome that
stopped the SNB key from entering to
cause disease," Dr Solomon says.
In fact, the resistant wheat varieties
had no lock at all and the research team
realised they were looking for an absence
of genes on the wheat genome, not the
presence of a true resistance gene.
"The finding was very surprising
and set us off on a completely different
path," Dr Solomon explains.
They discovered that SNB had the
capacity to trick susceptible wheats
into killing themselves and that this
trick worked only when the wheat
contained a specific gene. The opposite
of a resistance gene, this gene actually
resulted in susceptibility to the disease.
"The resistant plants have no such protein
recognition genes," Dr Solomon says.
PHOTO: KASIA CLARKE, ACNFP
Electron microscope image of Septoria nodorum blotch fungus invading a wheat leaf.
Mature spores can be seen inside the fluorescent green fruiting body.
Dr Solomon and his team are well on
the way to determining how SNB operates
at a molecular level and the wheat genes
that confer susceptibility to the disease.
"When the SNB pathogen lands on the
wheat leaf it penetrates the leaf surface
and produces a protein," Dr Solomon
explains. "If the wheat plant has a gene
that recognises this particular protein it
sets off a strong immune-like response
that kills the wheat leaf, enabling the
SNB pathogen, which requires dead tissue
to survive, to reproduce and spread.
"If the wheat plant does not have the
gene that recognises the pathogen protein
then the immune response does not
occur and SNB cannot survive, rendering
the plant resistant to the disease."
The ultimate goal of Dr Solomon's
research is to identify molecular markers
for the susceptible wheat gene so that
breeders can remove these genetics
from their breeding program.
"We need to determine the genes and
biochemical pathways that the fungus is
manipulating in the wheat genome so that
we can work out ways to block its activity."
To do this he has enlisted the help
of UK molecular scientists who have
the capacity to silence particular genes
using a specialised virus system.
"If we can silence the genes we think
are causing the susceptible disease response
then we will have validated our theory
and can start work on developing markers
for these genes," Dr Solomon says.
It is hoped that within three years
these markers will be available
to plant breeders for developing
SNB-resistant breeding lines.
SNB forms part of a group of diseases
known as necrotrophs that act against
plants in similar ways. Dr Solomon hopes
the work with SNB will transfer to the
development of resistant varieties for
other costly fungal diseases such as yellow
spot in wheat, net blotch in barley and
ascochyta in lentils and chickpeas. □
grdc research code anu00016
more information: Dr Peter Solomon,
Australian National University, 02 6125 3952,
peter.solomon@anu.edu.au